Gallium-nitride (GaN) is a commonly used Group IIIA-N material for electronic devices, where Group IIIA elements such as Ga (as well as boron, aluminum, indium, and thallium) are also sometimes referred to as Group 13 elements. GaN is a binary Group IIIA/V direct band gap semiconductor that has a Wurtzite crystal structure. Its relatively wide band gap of 3.4 eV at room temperature (vs. 1.1 eV for silicon at room temperature) affords it special properties for a wide variety of applications in optoelectronics, as well as high-power and high-frequency electronic devices.
GaN-based HEMTs are known which feature a junction between two materials with different band gaps to form a heterojunction (or ‘heterostructure’). The HEMT structure is based on a very high electron mobility, described as a two-dimensional electron gas (2DEG) which forms just below a heterostructure interface between a barrier layer (that typically comprises AlGaN) on a generally intrinsic active layer (that typically comprises GaN) due to the piezoelectric effect and a natural polarization effect. As with any power field effect transistor (FET) device, there is a gate, source electrode, and drain electrode, where the source electrode and the drain electrode each include contacts that generally extend through a portion of the barrier layer to form a low resistance ohmic contact with the underlying 2DEG in the surface of the active layer.
Known enhancement-mode (E-mode) Group IIIA-N HEMTs generally utilize a p-GaN layer between the metal gate and the barrier layer to provide enhancement-mode operation (threshold voltage (VT)>0, so normally off). Magnesium (Mg) is the usual p-type dopant specie used in Group IIIA-N materials for-doping this p-GaN layer.